docs: def update_value(self, uid, **kwargs):
          """
          Updates contact's custom field value.
          Returns :class:`Contact` object contains id and link to Contact.
  
          :Example:
  
          client.custom_fields.update_value(uid=1900901, contact_id=192012, value="abc")
  
          :param int uid:        The unique id of the CustomField to update a value. Required.
          :param int contactId:  The unique id of the Contact to update value. Required.
          :param str value:      Value of CustomField. Required.
          """
          contacts = Contacts(self.base_uri, self.auth)
          return self.update_subresource_instance(uid, body=kwargs,
                                                  subresource=contacts,
                                                  slug="update")